A matter of gravity

“Einstein’s theory triumphs!” So proclaimed the New York Times on Nov. 10, 1919, making Albert Einstein a celebrity. The headline referred to a stunning confirmation of one of relativity theory’s most audacious claims: that starlight is bent by the sun’s gravity. Einstein’s general theory of relativity, which depicts gravity as the curvature of space-time, had passed its first test.

ALL RELATIVE? Gravity Probe B has finished its measurements of the curvature of space-time surrounding Earth as a test of general relativity. NASA

Now, thanks to a data trove collected by a satellite called Gravity Probe B, scientists are poised to test Einstein’s theory more rigorously than ever before. Launched in 2004, the NASA probe features four gyroscopes sensitive enough to precisely measure two extraordinary effects predicted by general relativity (SN: 9/25/04, p. 206: Available to subscribers at Orbiting relativity test gets slow start). One effect is a tiny warping of nearby space-time by Earth’s gravity. The other, known as frame dragging, is Earth’s dragging of space-time along with it as the planet rotates. Physicists expect each effect to produce detectable drifts in the orientations of the gyroscopes’ axes relative to a reference star.

Late last month, the satellite completed its measurements and radioed to Earth the data that had been collected over 50 weeks. Principal investigator Francis Everitt of Stanford University, who helped conceive the mission 4 decades ago, estimates that it will take a year to analyze the information.

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